Gouge is a Rogue ability that incapacitates a target for four seconds and turns off the Rogue's auto-attack. It is used to remove targets from a fight for a short time, or as a desperate interrupt. With the talent Improved Gouge in the Combat tree, the duration is increased by .5/1/1.5 seconds, to a max of 5.5 seconds.
In PvE combat, Gouge has a variety of uses. Early on, it can be used to backstab a target if the Rogue is using daggers. Keeping the target unable to act for a period of time is useful to run away or bandage (though blind is better suited for bandaging). In the case of an add or unexpected aggro, Gouge can be used to buy a little time. If an enemy is casting a spell and kick is on cooldown, Gouge will also interrupt spellcasting. (Note that it's unusual for a PvE opponent to cast spells close enough that the second will complete before Kick is ready to use.)
Placeholder - not good enough at PvP to say